1. Field of the Invention
This invention relates generally to electrical switchgear and protection arrangements for electric power distribution networks. More particularly, the invention relates to an improved isolating circuit breaker and a circuit protection system for medium voltage distribution networks utilising a plurality of the improved isolating circuit breakers.
2. Discussion of the Background Art
Existing electrical switchgear includes a dual purpose assembly that may function as both an isolating switch and a fuse, and is generally known in the electric power industry as a xe2x80x9cdropout fusexe2x80x9d. Examples of a fuse and a dropout fuse holder are disclosed in Australian Patent No. 667953 and Australian Patent No. 683191 (respectively), both in the name of Cooper Power Systems, Inc. Some of the problems and drawbacks of conventional fuses and associated fuse holders are discussed in the introductory paragraphs of the Cooper Power Systems patent specifications.
Electric power utilities generally use dropout fuses in relatively large numbers in medium voltage distribution networks, often in a pole-mounted configuration, for reasons of cost. However, the fuses must be manually replaced by linesmen, which delays restoration of supply subsequent to a fuse blowing. Isolating switches, with or without fuses, are used for operations in conjunction with separate line sectionalising circuit breakers or automatic re-closing type circuit breakers. In the present context, medium voltage includes the range from about 10 kV up to about 75 kV. There have also been previous attempts to combine on-load circuit breakers with isolating switches, as exemplified by U.S. Pat. No. 4,596,911 to Guery et al., wherein a common operating mechanism closes the isolating switch prior to the circuit breaker and vice versa during opening.
More recently, U.S. Pat. No. 5,959,398 to McKean describes a sequential isolating circuit breaker and actuator wherein a vacuum interrupter provides fast interruption of load current and the isolator provides a large visual gap in the open position for safety reasons. The actuator mechanism in the McKean patent is a complex rotary driven arrangement including spring loaded levers and lost motion linkages.
German Patent Application No. 3412399 in the name of Sachsenwerk, Licht and Kraft AG discloses a high voltage switch with a vacuum switching tube incorporated into a rotary arm carrying an isolating contact on the end of the arm. The rotary mounting for the other end of the rotary arm, that is driven by an actuator, has a cam slot and guide pin arrangement for synchronising the opening of the vacuum interrupter contacts with the isolator contacts.
The prior art arrangement of isolating switches and circuit breakers in series with common actuation does not allow for independent operation of the respective contact sets. In particular, this arrangement does not facilitate opening and automatic re-closing of the circuit breaker alone, to reconnect the load in the event of a transient fault on a protected line. Furthermore, the physical designs are generally suited to metal-clad or indoor use, rather than being more compact and suited to pole-mounting.
In distribution networks with three phase circuits it is desirable to detect faults such as a phase-to-phase fault or a phase-to-ground fault, that may compromise distribution network security. Fault detection can be arranged to control operation of circuit breakers associated with the conductors in order to prevent network damage and when endeavouring to clear the fault.
In obtaining measurements from phase conductors, substantial isolation arrangements are required in view of the potential difference which exists between individual phase conductors and the control equipment for circuit breakers. Conventionally control equipment for circuit breakers is mounted in a cabinet at ground potential.
Furthermore, circuit breakers for three-phase applications typically employ a common actuating mechanism for all three phases. This similarly calls for a relatively heavy and cumbersome device, resulting from the isolation requirements and the mechanical performance required to operate three sets on contacts. This also adds to the cost of acquiring and installing circuit breakers.
Object of the Invention
It is an object of the present invention to provide an isolating circuit breaker which ameliorates or overcomes at least some of the problems associated with the prior art.
It is another object of the present invention to provide a compact isolating circuit breaker for pole mounted, medium voltage applications.
It is yet another object of the present invention to provide a self-contained isolating circuit breaker which can be retrofitted to electrical distribution networks in place of conventional dropout fuses and fuse holders.
It is a further object of the invention to provide a circuit protection arrangement including a plurality of isolating circuit breakers that effect coordinated protection of three phase circuits.
Further objects will be evident from the following description.
Disclosure of the Invention
In one form the invention resides in an isolating circuit breaker for pole mounting in relation to a electrical distribution line, said isolating circuit breaker including:
(a) an isolating switch with a pivoting link, said isolating switch having respective terminals for electrical coupling to load and supply conductors of the electrical distribution line;
(b) a circuit interrupter disposed in series with the isolating switch, intermediate said load and supply conductors;
(c) an actuator arranged for selectively opening and closing the circuit interrupter;
(d) an electronic controller controlling operation of the circuit breaker in response to electrical conditions in the distribution line; and
(e) said isolating switch, circuit interrupter, actuator and electronic controller arranged together on a mounting structure adapted for pole mounting.
Most preferably, the circuit interrupter is incorporated in the pivoting link of the isolating switch.
In one arrangement of the isolating circuit breaker the electronic controller is incorporated in the mounting structure; whilst in an alternative arrangement the electronic controller is incorporated in the pivoting link of the isolating switch.
The actuator and electronic controller are suitably not isolated from the distribution line so as to float at line potential. If required however, the actuator and electronic controller could be isolated from the distribution line.
Preferably the isolating circuit breaker further includes a sensor arrangement coupled to the electronic controller, the sensor arrangement arranged for producing signals in response to electrical conditions in the distribution line. In preference, the sensor arrangement is carried by the mounting structure. Suitably the sensor arrangement includes a current transformer for measuring current in the distribution line. The sensor arrangement may also include a voltage transformer for measuring voltage in the distribution line. If required, the sensor arrangement includes a resistive voltage divider or a capacitive voltage divider for measuring voltage in the distribution line.
The electronic controller may derive power supply from the distribution line. The electronic controller may derive power supply from a separate transformer or capacitor coupled to the distribution line. In preference, the electronic controller derives power supply from a primary or secondary storage cell.
The electronic controller preferably includes a integrated circuit device, such as a microprocessor, gate array or applications specific integrated circuit, with a memory for storing data. Preferably the data includes protection settings relating to operation of the isolating circuit breaker. Suitably the settings include parameters for an automatic re-closing sequence of the circuit interrupter. If required, the memory may also be arranged to store historical data relating to the electrical conditions in said distribution line.
The circuit interrupter may further include at least one communications transceiver coupled to the electronic controller. Preferably the communications transceiver facilitates communications with other isolating circuit breakers for providing earth current and/or earth fault protection of a multi-phase distribution circuit. If required, the communications transceiver facilitates communications with a remote device for uploading protection settings and/or downloading of historical data.
Preferably, the communications medium utilised by the communications transceiver is radio. If required the communications medium may be optical, suitably utilising optical fibre links. Alternatively, the communications medium may be acoustic, preferably in the ultrasonic range of frequencies.
Suitably, the isolating switch is an air gap isolator. Preferably the circuit interrupter is a vacuum interrupter.
In a second form, the invention resides in an isolating circuit breaker for pole mounting in relation to a electrical distribution line, said isolating circuit breaker including:
(a) a mounting arrangement comprising an insulating housing;
(b) a first line terminal on the housing for connection to a supply conductor of the distribution line;
(c) a first isolating contact electrically coupled to the first line terminal;
(d) a sensor arrangement located in said housing, the sensor arrangement producing signals in response to electrical conditions in the distribution line;
(e) a control module located in said housing, the control module receiving signals from the sensor arrangement for controlling operation of an actuator in response to said signals;
(f) a link pivotally mounted in relation to said housing, the link having a second isolating contact on a free end thereof for engagement with the first isolating contact;
(g) the link incorporating a circuit interrupter selectively opened and closed by the actuator; and
(h) wherein said circuit interrupter has a terminal electrically coupled to the second isolating contact and has an opposite terminal electrically coupled to a second line terminal for connection to a load conductor of the distribution line.
Suitably the sensor arrangement is associated with a portion of the electrical coupling between the first line terminal and the first isolating contact, which portion is also located in said housing.
Electronic circuitry for the control module may be disposed in a separate cartridge that is selectively removable from the insulating housing for adjusting the operating parameters and/or downloading data logs.
Preferably, the actuator includes an operating arm protruding from the insulating housing for opening and closing said circuit interrupter.
The actuator may comprise a solenoid mechanically coupled to the operating arm. Most preferably the operating arm is manually operable, suitably by a separate lever which may also functions as a position indicator for the circuit interrupter.
In a third form the invention resides in an isolating circuit breaker for pole mounting in relation to a electrical distribution line, said isolating circuit breaker including:
(a) a mounting arrangement comprising two insulating members carrying respective support arms;
(b) a first line terminal on an upper support arm for connection to a supply conductor of the distribution line;
(c) a first isolating contact on the upper support arm electrically coupled to the first line terminal;
(d) a link pivotally mounted on a lower support arm, the link having a second isolating contact on a free end thereof for engagement with the first isolating contact;
(e) the link incorporating:
(i) a sensor arrangement for producing signals in response to electrical conditions in the distribution line,
(ii) a controller receiving signals from the sensor arrangement for controlling operation of an actuator in response to said signals, and
(iii) a circuit interrupter selectively opened and closed by the actuator;
(f) wherein said circuit interrupter has a terminal electrically coupled to the second isolating contact and has an opposite terminal electrically coupled to a second line terminal for connection to a load conductor of the distribution line.
Suitably the sensor arrangement is associated with the electrical coupling between the circuit interrupter and the second isolating contact.
The actuator is preferably a magnetic actuator with an axially movable operating member.
The circuit interrupter is suitably a vacuum interrupter having fixed and movable contacts coupled to respective fixed and movable terminals.
Suitably, the fixed terminal of the circuit interrupter is pivotally mounted on the lower support arm and the movable terminal is coupled to the actuator. The circuit interrupter may also be manually operated by an operating lever mechanically coupled to the actuator.
If required the operating lever operates the circuit interrupter during a first arc of travel, and opens the first and second isolating contacts of the isolating switch during a second arc of travel. Desirably, the circuit interrupter is only able to be closed after the first and second isolating contacts of the isolating switch are closed.
In further form, the invention resides in a circuit protection arrangement for a multi-phase circuit of an electrical distribution network, said arrangement comprising:
(a) a plurality of isolating circuit breakers for connection in respective phase lines of the multi-phase circuit, wherein each isolating circuit breaker includes:
(i) an isolating switch with a pivoting link, said isolating switch having respective terminals for electrical coupling to load and supply conductors of a phase line;
(ii) a circuit interrupter disposed in series with the isolating switch, intermediate said load and supply conductors;
(iii) an actuator arranged for selectively opening and closing the circuit interrupter;
(iv) a sensor arrangement producing signals in response to electrical conditions in a respective phase line;
(v) a communications transceiver for transmitting said signals to others of the plurality of isolating circuit breakers and for receiving respective phase line condition signals transmitted by other isolating circuit breakers of said plurality;
(vi) an electronic controller receiving signals from both the sensor arrangement and from the other isolating circuit breakers via the communications transceiver; and
(vii) said isolating switch, circuit interrupter, actuator and electronic controller arranged together on a mounting structure adapted for pole mounting;
(b) whereby the electronic controllers process the line condition signals from each phase in substantially real time to control operation of individual actuators of respective circuit interrupters.
Preferably, the communications transceiver uses an electromagnetic communications medium, suitably employing an analogue modulation scheme. The communications medium may comprise radio, or alternatively, the communications medium may comprise optics. In an alternative arrangement, the communications transceiver uses an acoustic communications medium such as ultrasonic band frequencies.
Suitably, the signals produced by the sensor are indicative of the instantaneous value of the current and/or voltage on each phase line. Preferably, the control modules sum the instantaneous values whereby a residual vector sum is indicative of a fault condition in the multi-phase circuit.
In a yet further form the invention resides in a circuit protection arrangement for a multi-phase circuit of an electrical distribution network, said arrangement including:
(a) a plurality of isolating circuit breakers for connection in respective phase lines of the multi-phase circuit, wherein each isolating circuit breaker comprises:
(i) an isolating switch with a pivoting link, said isolating switch having respective terminals for electrical coupling to load and supply conductors of a phase line;
(ii) a circuit interrupter disposed in series with the isolating switch, intermediate said load and supply conductors;
(iii) a sensor arrangement producing signals in response to electrical conditions in a respective phase line;
(iv) an electronic controller receiving signals from the sensor arrangement,
(v) an actuator arranged for selectively opening and closing the circuit interrupter in response control signals from the electronic controller; and
(vi) said isolating switch, circuit interrupter, actuator and electronic controller arranged together on a mounting structure adapted for pole mounting;
(b) the actuators of respective isolating circuit breakers being mechanically coupled such that all circuit interrupters of said plurality may be opened substantially simultaneously in response to a predetermined fault condition in at least one of said phase lines.
The mechanical coupling may be arranged such that all circuit interrupters are opened simultaneously only as a result of a persistent fault condition, for example at the end of an automatic re-closing sequence. Suitably, the operating mechanisms are mechanically coupled by insulating coupling rods extending between respective actuators.
In a still further form, the invention resides in a method for protecting a multiphase circuit of an electrical distribution network, said network comprising:
(a) a plurality of isolating circuit breakers for connection in respective phase lines of the multi-phase circuit, wherein each isolating circuit breaker includes:
(i) an isolating switch with a pivoting link, said isolating switch having respective terminals for electrical coupling to load and supply conductors of a phase line
(ii) a circuit interrupter disposed in series with the isolating switch intermediate said load and supply conductors;
(iii) a sensor arrangement producing signals in response to electrical conditions in the phase line;
(iv) a communications transceiver associated with the sensor arrangement; and
(v) the isolating switch, circuit interrupter and sensor arrangement carried by a mounting structure adapted for pole mounting;
(b) wherein the method includes the steps of:
(i) sensing the instantaneous values of an electrical parameter of a phase line at a respective isolating circuit breaker;
(ii) transmitting the instantaneous value signals produced by the sensor arrangement to others of the plurality of isolating circuit breakers and receiving respective instantaneous value signals transmitted by the other circuit breakers;
(iii) summing the instantaneous value signals from the sensors in each circuit breaker in substantially real time; and
(iv) controlling operation of individual actuators of respective circuit interrupters in accordance with the sum of said instantaneous value signals.